Discharge tube having an indirectly heated cathode



30, 1932- J. G. w. MULDER 1,875,106

DISCHARGE TUBE HAVING AN INDIRECTLY HEATED CATHODE Filed Nov. 15, 1930 INVENTOR J.6.W. MULDER ATTORN EY Patented Aug. 30, 1932 I UNITE STAES J OI-IANN ES GYSBERTUS WILI-IELM MULDER, 0F EINDI-IOVEN, NETHERLANDS, ASSIGNOR TO RADIO CORPORATION OF AMERICA, A CORPORATION OF DELAWARE DISCHARGE TUBE HAVING AN INDIRECTLY. HEATED CATHODE Application filed November 15, 1930, Serial No. 495,806, and in the Netherlands January 22, 1930.

This invention relates to discharge tubes having an indirectly heated cathode.

Indirectly heated cathodes are known in which the heating element is freely mounted within a metal envelope constituting the cathode proper, the envelope itself consisting of an emitting material or being coated with an emitting substance. Furthermore, cathodes are known in which a body made of insulating material is provided with passages in which a filament is laid, or in which the plastic in sulating material is kneaded around the filament so as to surround it entirely, and subsequently hardened. Furthermore, the outer side of this insulating body is provided with the cathode proper, consisting, for example, of a metal case which is coated with barium oxide.

In these known constructions it takes a considerable time before the cathode is heated to a sufficient temperature, which is especially the case with large incandescent cathodes,

I such as, for example, cathodes of the type as are frequently used in rectifiers for great current intensities. Moreover, in the known constructions there is a risk of the cathode being unequally heated due to the fact that there lies much insulating material having poor heat conducting properties between the incandescent body and the cathode, so that there is a great risk of the heat being unevenly distributed.

According to the present invention, these diiiiculties are avoided, while in addition a very simple and practical construction of an indirectly heated cathode is established. This may be obtained by constituting the cathode of a body made of conducting material, which is provided with a plurality of passages in which heating wires are arranged which are electrically insulated from the conducting body.

Due to the fact that the heating wires directly pass through passages provided in a conducting body, for instance of metal, the emitting surface of this body will be very quickly and uniformly heated due to the 'great conducting capacity of the metal.

Preferably theconducting body is provided With'an accidented surface, to which a substance having a highly electron emitting capacity is applied.

In a very suitable embodiment the body is shaped as a hollow cylinder, whose annular end surfaces are connected by passages through which the heating wires are slipped. Preferably, the inner wall of thecylinder is coated with a substance having a highly electron emitting capacity. One advantage of this construction consists in that the inner wall of such a cylinder will be heated to a higher temperature than the outer wall, so that the heat is more economically utilized if the emitting layer is applied thereto.

For the application of the substance having a highly electron emitting capacity use may be made of a helically wound wire which is laid on the inner or outer surface of the metal cylinder. The heating wires may be insulated from the conducting body by means of tubes made of steatite which are placed in the bores ofthis body.

The invention will be more clearly understood by reference to the accompanying drawing, representing, by way of example, one embodiment thereof.

Fig. 1 is a perspective view of an indirectly heated cathode according to the invention.

Fig. 2 is a longitudinal section of this cathode.

Fig. 3 is a cross section of the cathode, and

Fig. 4 shows the cathode mounted in a rectifying tube having two anodes.

As shown in the drawings, several passages 2 are provided in a hollow cylindrical body 1 consisting of conducting material, for example, nickel. By these passages 2 which are uniformly arranged in the cylindrical body, both end surfaces of the cylinder are connected. In the passages, tubes 8 of insulating, highly refractory material, for example, steatite, are provided. Through these successive tubes one single heating wire 4 is led back and forth.

The inner wall of the cylinder is coated with a layer 5 of a highly electron-emitting substance consisting, for example, of one or more of the oxides, carbides, or silicates of barium, strontium, ceasium, rubidium, and so forth. As appears from the section, the inner 1 wallof the cylinder is roughened, so that the emitting layer adheres better thereto. This inight be also obtained by providing the surface-to which the emitting layer is applied with a helically wound wire.

,In Fig. 4s'the, cathode 1 is mounted on two supporti'ng wires6 and 7, the latter serving at the same time as pole wire. The currentis supplied to the heating wire through the. leading-in wir'esfS and 9; Forclearness"sakej," y these wires are only partly represented on the drawing. Near theends-of the cathode two anodes 10 and llare arranged which are supported by thewires 12'and 13 servingatvthe same time as leading-in wires;

a The invention may be applied to exhausted tubesas well as to gas-filled ones. Iclaim: j p 1. An electron discharge device comprising a sealedenvelope encloslng an anode and a cathode comprising a tubular conducting body having a plurality of passages extend- 'ing' atubular metal body having in its wall a plurality of passages eXten-ding-longitudt ing through said body between its annular end surfaces, and an'insulated heater wire in said passages. r g

" 2. An electron'emitting cathode'comp'ris nallyo'f said body from one annular end surface ,to the other, an insulated heater wire strung back and forth through said passages,

andan elec ron emitting layer on the-interior wall of said body.

, 3. An electron emitting cathode compris- I ing a tubular'conducting body having in its wall a plurality of passages symmetrically disposed about and'parallel to the longitudie nal axis of-saidbody andextending from one end of said bodyto the other, heater'wires in 7 said passages, refractory insulation between said heater wires and said body,and an elect tron emitting layer on the inner wall of said body.

4: ing a tubular conducting body, an electron emitting layer on the inner Wall of said body,

and a plurality of heater wires extending parallel to and symmetrically disposed about theiongitudinal a-Xis of said body outside the inner wall of said body, and electrically in? sulated from but ingood heat conductive relation to sa d body;

5. 'An electron emitting cathode comprising a tubular conducting body, an electron emitting layer on the inner wall of said body, and a plurality of insulated heated wires embedded in said body and symmetrically dis V posed about and parallel to the longitudinal axis of said body.

' JOHANNES cYsBrRrus WILHELMMULDER.

An electron emitting cathode compris- 

